The first challenge is getting the app installed. If you attempt to download Messenger directly from the Google Play Store on an Android 5.1 device today, you may hit a wall. Facebook frequently updates the app’s minimum API requirements, often pushing older OS versions into obsolescence.
Most users on Android 5.1 will need to sideload an older APK (Android Package Kit) from a third-party mirror (like APKMirror or Uptodown). This immediately puts the user at a slight security disadvantage, as you aren't running the absolute latest build, and you lose automatic updates. Messenger Apk Android 5.1
If you also have the main Facebook app, remove it. It constantly runs services that conflict with Messenger. Use Facebook Lite or the mobile web version instead. The first challenge is getting the app installed
⚠️ Warning: Avoid random "Messenger APK" websites. Many contain malware, ads, or require dangerous permissions. Stick to APKMirror. ⚠️ Warning: Avoid random "Messenger APK" websites